PDCD1 and breast cancer: Similarly, S. Muenst et al. suggested that PD-L1 expression in breast cancer specimens is associated with larger tumor size, more advanced tumor process, and a positive lymph node status, which may suggest that involvement of PD-1/PD-L1 pathway may contribute to the immune escape, thereby influencing the rate of proliferation and spreading more rapidly (Muenst et al., 2014).